This invention relates to a proton exchange membrane (PEM) fuel cell in which the edge seals of the cathode and/or anode diffusion layers are formed by folding over corresponding portions of the membrane.
As is known, a PEM fuel cell has catalyst layers on the cathode and anode side of the membrane, possibly with optional diffusion layers formed as a coating on the cathode and anode substrates, respectively, which are on the non-membrane side of the cathode and anode catalysts. The substrates, also known as carbon papers, are highly porous, which may, for instance, have on the order of 70% porosity with pores on the order of 30 microns in diameter. In order to prevent the oxidant reactant gas (such as air) and the fuel reactant gas (such as a hydrogen containing gas) from escaping through the side edges (those edges not in communication with the respective manifolds) it has been known to provide edge seals to the anode and cathode substrates.
In FIG. 1, an exemplary PEM fuel cell 9, of the general type known to the prior art, includes a proton exchange membrane 11, an anode catalyst 12 which may comprise a coating on the membrane of on the order of 10 micron thickness, an anode substrate 14, which may, optionally, have an anode diffusion layer comprising a coating 15 on the order of 25 microns on the surface of the substrate 14. The fuel flow field may typically comprise an anode flow field water transport plate 18 having fuel reactant gas flow channels 19 therein and a degree of porosity to permit water, typically from a coolant flow channel (not shown), to be absorbed in the fuel reactant gas so as to provide moisture through the anode layers to the membrane 11. Similarly, on the cathode side, there is a cathode catalyst 22, there may be an optional cathode diffusion layer 23, a cathode substrate 26, and an oxidant reactant gas flow field, typically comprised of a cathode flow field water transport plate 27 having oxidant reactant gas flow field channels 28 therein. In FIG. 1, the fuel reactant gas manifold (not shown) will be in fluid communication with the fuel reactant gas flow field channels 19, and the oxidant reactant gas manifold (not shown) will be in fluid communication with the oxidant reactant gas flow field channels 28.)
Interfacial seals between the anode water transport plate 18 and the anode substrate 14, as well as between the cathode water transport plate 27 and the cathode substrate 26 may typically comprise beads of silicon rubber 31, 32, respectively.
To prevent gases from leaking from the substrate layers 14, 26, it is common to employ an edge seal 35, 36 which consists of a thermoplastic film such as polyvinylidene (KYNAR(copyright)), or an elastomer, such as a silicone rubber, extruded into the substrate. However, the extrusion process is carried out with only a single substrate at one time, and requires use of a hot laminating press, press shims, release films and a dwell time of minutes. The process therefore does not lend itself well to high speed production which would be required for low cost fuel cells suitable for use in vehicles.
Thermoplastic films 33 may be provided as fillers at the edges of the anode and cathode catalysts and optional diffusion layers.
Fuel cells of the type described with respect to FIG. 1 are illustrated in U.S. Pat. Nos. 6,020,083, 6,159,628, and 6,187,466.
Objects of the invention include: provision of an improved PEM fuel cell substrate gas edge seal; a PEM fuel cell substrate gas edge seal which can be provided on a high speed production basis; and a low cost and effective PEM fuel cell substrate gas edge seal.
According to the present invention, the proton exchange membrane of a PEM fuel cell is provided with at least one pair of flaps which are wrapped around the edges of the cathode substrate and/or the anode substrate of each fuel cell to provide a substrate edge seal.
According further to the invention, liquified adhesive may be applied to the membrane flaps before they are folded over the substrate so as to provide improved adhesion to the substrate and provide an improved substrate edge seal.
Other objects, features and advantages of the present invention will become more apparent in the light of the following detailed description of exemplary embodiments thereof, as illustrated in the accompanying drawing.